1. Field of the Invention
The present invention relates to a method of fixing an insertion electrode panel in a compression-bonded semiconductor device. More specifically, it relates to an improvement in a method of fixing an insertion electrode panel in a compression-bonded semiconductor device such as a compression-bonded power thyristor, in which the insertion electrode panel is overlapped on a semiconductor element.
2. Description of the Prior Art
As a power thyristor has become of a larger capacity in recent years, the diameter of the silicon substrate of an element employed therein has become as large as about 90 to 102 mm. Further, since such a thyristor is applied to a high-frequency device, it is extremely important to increase initial turn-on areas, i.e., to increase the turn-on speed as much as possible.
As means for increasing the initial turn-on areas, there is generally employed a method in which an auxiliary thyristor is provided in the vicinity of a gate electrode so that the auxiliary thyristor is first turned on, thereby to turn on the main thyristor region. Further, in view of wide-ranged use of the device, means is employed to incorporate such an auxiliary thyristor into the main thyristor, whereon the structure is complicated for facilitating turning-on of the main thyristor.
As another technical means for ensuring large capacity of a thyristor, there is employed a method of bringing a thyristor element and an outer electrode disc member into pressure contact with each other, in which a relatively thin insertion electrode panel is inserted between the electrode of the inner thyristor element and the outer electrode disc for bringing the same into pressure contact with each other and carrying a current to the same.
FIG. 1 is a perspective view showing a semiconductor element and an insertion electrode panel before coupling by a conventional fixing method, and FIG. 2 is a roughly illustrated cross-sectional view showing an example of a compression-bonded thyristor assembled by sealing the semiconductor element to which the insertion electrode panel as shown in FIG. 1 is fixed.
Referring now to FIGS. 1 and 2, description is made with respect to a conventional method of fixing an insertion electrode panel to an element of a compression-bonded thyristor. A thyristor 1 has on its smoothed surface a gate electrode 2 provided in the central position thereof and an electrode pattern 3 of an auxiliary thyristor formed radially from the central position. An insertion electrode panel 4 is formed by a thin panel of conductive metal such as molybdenum, tungsten, kovar (alloyed stone), silver and copper, and is connected to an electrode (cathode) overlapped on the thyristor element 1 in a compression-bonded manner. The insertion electrode panel 4 is provided with a pattern hole 5 which corresponds in form to the electrode pattern 3 for receiving the same.
The insertion electrode panel 4 is overlapped on the thyristor element 1 in a close contact manner, and a passivation rubber member 6 is attached to the outer circumferential portion thereof to be hardened, whereby the insertion electrode panel 4 is fixed to the thyristor element 1. Under this condition, the thyristor element 1 is held from below by an electrode disc (anode) 7 of copper etc. and from above by an outer electrode disc (cathode) 8 of copper etc. through the insertion electrode panel 4 to be compression-bonded with the same. The compression-bonded thyristor element 1 and the insertion electrode panel 4 are then sealed by enclosing the side circumferential portion of the thyristor element 1 by an insulating enclosure 9 of, e.g., ceramic material. A contact ring 10 of, e.g., copper is brought sealingly into contact with the lower portions of the outer electrode disc 7 and the insulating enclosure 9 and fixed thereto by brazing. A coupling flange 11 made of a metal plate is fixed in an airtight manner to the upper portion of the insulating enclosure 9. The coupling flange 11 is coupled in an airtight manner, by welding etc., with another coupling flange 12 of a metal plate, which is airtightly fixed to the outer electrode disc 8.
It is to be noted that a gate lead wire and means for withdrawing the same are not shown in FIG. 2.
In the aforementioned conventional method of fixing the insertion electrode panel 4, there have been the following disadvantages: When the insertion electrode panel 4 is overlapped with the thyristor element 1 with the pattern hole 5 aligned with the electrode pattern 3 and the passivation rubber member 6 is fixed to the same to be hardened, displacement may take place between the pattern hole 5 and the electrode pattern 3 during the hardening process of the passivation rubber material. Further, when the electrode pattern 3 is made complicated, it is difficult to align the pattern hole 5 with the same by hand. In addition, the insertion electrode panel 4 is slightly larger in outer diameter than the electrode pattern 3 of the thyristor element 1 to ensure current carrying capacity and the inner contact surface of the outer electrode disc 8 is conformed in outer diameter to the insertion electrode panel 4, whereby merely a small amount of the passivation rubber member 6 is employed for fixing the insertion electrode panel 4. Thus, the insertion electrode panel 4 cannot be reliably fixed to the thyristor element 1, leading to displacement from the same.
Although projections and recesses for alignment may be provided in the contact surfaces of the insertion electrode panel 4 and the thyristor element 1, the surface of the insertion electrode panel 4 is smoothly formed for facilitating electric contact and is made extremely thin within the range of 0.2 to 0.5 mm for preventing electric resistance loss, and hence it is not possible to provide projections or recesses for alignment on the same. In correspondence thereto, further, it is extremely difficult to provide engaging projections or recesses on the smooth upper surface of the thyristor element 1.
Thus, in the conventional fixing method, the insertion electrode panel 4 might be displaced from the thyristor element 1 during assembling and after completion of the assembling operation.